3-O-methyl-D-glucose (3MeG) is a hexose which competes with glucose for the placental facilitated diffusion transport system. 3MeG is not metabolized. Using the chronically catheterized near-term sheep we will describe the effects of maternal plasma insulin and glucose concentration on the placental clearance of 3MeG. We will also describe the effect of fetal plasma insulin and glucose concentrations on the placental clearance of 3MeG. These experiments will be performed using "glucose clamp" and "insulin clamp" techniques. With these techniques one variable remains constant while the other is permitted to change in a controlled manner. We will also measure the maximum possible placental clearance that could be obtained in these preparations (Cmax) and the degree of diffusion limitation (LD) for 3MeG. A mathematical model will be developed in which the data acquired in the above experiments will be synthesized such that they can be used to develop algorithms from which the placental transfer of 3MeG can be predicted under a range of maternal and fetal insulin and glucose concentrations. Information obtained from these experiments will assist in our understanding of the dynamics of placental glucose transfer and may shed some light on some of the problems associated with maternal diabetes during pregnancy.